Setting Radiation Requirements
on the Basis of Sound Science:
The Role of Epidemiology
INFO-0812
March 2011
Setting Radiation Requirements on the Basis of Sound Science:
The Role of Epidemiology
© Minister of Public Works and Government Services Canada 2011
Catalogue number CC172-66/2011E-PDF
ISBN 978-1-100-17762-5
Published by the Canadian Nuclear Safety Commission (CNSC)
Catalogue number: INFO-0812
Extracts from this document may be reproduced for individual use without
permission provided the source is fully acknowledged. However, reproduction
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written permission from the Canadian Nuclear Safety Commission.
Également publié en français sous le titre de : Établissement d’exigences
de radioprotection selon des principes scientifiques éprouvés : le rôle de
l’épidémiologie
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Web site: nuclearsafety.gc.ca
FoRwaRD
Epidemiology is the study of the distribution and determinants of diseases in human populations. It serves
as the foundation for public health and preventive medicine and is based on observations, rather than on
experiments.
The purpose of this document is to describe the role of epidemiological research in setting radiation protection
requirements, part of the mandate of the Canadian Nuclear Safety Commission (CNSC). The CNSC regulates
the use of nuclear energy and materials to protect workers, the public and the environment.
This document presents the main types of epidemiology studies, key studies which form the basis of our
understanding of radiation risk (i.e., Atomic bomb survivors, radiotherapy patients, people exposed during
the Chernobyl accident, nuclear energy workers and uranium miners) and regulatory requirements for
radiation protection.
It summarizes CNSC’s assessment of the health effects of the past and present radium and uranium refining
and processing industries in Port Hope, CNSC’s assessment of the health effects of tritium, and CNSC’s
assessments of radon risk among uranium miners. It also discusses studies of people living near nuclear
facilities both in Canada and around the world.
The document discusses the role of national and international expert committees like the united Nations
Scientific Committee on the Effects of Atomic Radiation (uNSCEAR) and the National Academy of
Science’s Biological Effects of Ionizing Radiation (BEIR) Committee that review and summarize current
radiation research. It also discusses the work of the International Commission on Radiological Protection
(ICRP) that makes radiation protection recommendations for workers and the public.
The CNSC uses epidemiology and a wealth of other radiation science to protect the health of Canadians.
The CNSC bases its risk assessments for populations exposed to low dose levels of ionizing radiation on the
linear no-threshold (lNT) model. This model assumes a direct and proportional relationship exists between
radiation dose and cancer (i.e., an individual’s likelihood of cancer increases in proportion to his/her radiation
dose). However, at doses below 100 millisieverts (mSv), it is not possible to distinguish cancer due to radiation
from that of the natural variation of the disease among the general population.
Although recent radiobiological findings indicate that cellular repair processes could happen at low doses,
these findings are not understood well enough to trigger changes to the current regulations. The lNT model is
still supported by data from both epidemiology and radiobiology and provides a conservative, precautionary
assessment of radiation risk at low doses.
The CNSC sets radiation protection requirements on the basis of sound science. In so doing, the CNSC
effectively limits radiation exposures as a result of the nuclear industry to protect the health of Canadians.
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SETTING RADIATION REquIREMENTS ON THE BASIS OF
SOuND SCIENCE: THE ROlE OF EPIDEMIOlOGy
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TaBLE oF CoNTENTS
FORWARD 1
1.0
INTRODuCTION
4
2.0
SOuRCES OF IONIZING RADIATION IN EVERyDAy lIFE
5
3.0
OVERVIEW
7
3.1
What is Epidemiology?
7
3.2
The Three Main Types of Epidemiological Studies
8
3.2.1
Cohort Studies
8
3.2.2
Case-Control Studies
8
3.2.3
Descriptive Ecological Studies
8
3.3
4.0
9
3.3.1
What is Causation? Does Factor A Cause Disorder B?
9
3.3.2
What is Correlation?
9
3.3.3
Errors that have an Impact on the Accuracy of Risk Estimates in Epidemiology
10
STuDIES ON WHICH EPIDEMIOlOGICAl EVIDENCE OF
RADIATION HEAlTH EFFECTS IS BASED
11
4.1
Atomic Bomb Survivors life Span Study
11
4.2
The Chernobyl Accident
11
4.3
Patients Treated with Radiotherapy for Non-Cancer Diseases
12
4.4
Miners Exposed to Radon Decay Products
12
4.5
Effects of Radiation on Nuclear Energy Workers – IARC 15-Country Study
13
Summary
13
4.6
5.0
Causation
EPIDEMIOlOGICAl STuDIES OF PEOPlE lIVING NEAR NuClEAR
POWER PlANTS OR uRANIuM PROCESSING FACIlITIES
14
5.1
Offspring of Ontario Hydro Workers
14
5.1.1
Childhood leukaemia
14
5.1.2
Birth Defects
14
5.2
Communities Near Nuclear Facilities in Ontario
14
5.3
Health Studies in the Port Hope Community
15
5.4
Communities Near Gentilly-2 in québec
16
5.5
Summary
17
5.6
5.7
5.8
6.0
7.0
Communities living Near German Nuclear Facilities
17
5.6.1
Studies Conducted Around Nuclear Power Plants
17
5.6.2
Case-Control Study on leukaemia in German Children (KiKK)
17
5.6.3
The German Radiological Protection Commission
18
5.6.4
Reviews of Studies of Childhood leukaemia Around Nuclear Facilities
19
Committee on Medical Aspects of Radiation in the Environment Reports
19
5.7.1
Childhood leukaemia Around Nuclear Power Plants
19
5.7.2
Effects of Radiation on Offspring of Nuclear Workers
19
Summary
20
INTERNATIONAl GROuPS OF ExPERTS IN RADIATION PROTECTION 21
6.1
united Nations Scientific Committee on the Effects of Atomic Radiation
21
6.2
The Biological Effects on Ionizing Radiation Committee
21
6.3
The International Commission on Radiological Protection
22
6.4
The International Atomic Energy Agency
22
DISCuSSION AND CONCluSIONS
7.1
How Does the CNSC use Epidemiology To Protect Nuclear Workers and the Canadian Public?
REFERENCES 23
23
25
1.0
INTRoDUCTIoN
The Canadian Nuclear Safety Commission (CNSC) regulates the use of nuclear energy and materials to
protect workers, the public and the environment.
In order to manage radiation risks and to set regulatory limits that will protect workers and the public from
ionizing radiation, CNSC has first to assess the risks that are present.
The assessment of radiation risks involves many steps and requires the input of several disciplines such
as physics, radiobiology, genetics, and epidemiology. The combination of these different disciplines will
contribute to the estimation of the risk.
The main discipline involved in the assessment of human health risks from radiation exposure is epidemiology.
Several epidemiological studies of populations exposed to radiation have been conducted to assess these risks
and they are considered the best source of evidence on which the current models used in radiation protection
have been based.
The CNSC has produced this document to help explain how epidemiology is used in radiation risk assessment.
It describes the different types of epidemiological studies used to assess health risks from radiation, and
highlights key studies that have laid the foundation for international radiation protection models. It also
describes how world experts work together to share and review scientific studies on radiation health effects
that are further used to set the radiation protection recommendations adopted by regulatory agencies
internationally. Finally, this document discusses how CNSC uses epidemiology to protect nuclear workers and
the Canadian public.
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2.0
SoURCES oF IoNIZING RaDIaTIoN IN EVERYDaY LIFE
According to the International Agency for Research on Cancer, ionizing radiation is perhaps one of the most
studied causes of cancer. Multidisciplinary research (such as radiobiology, genetics, molecular biology, physics,
chemistry, and biochemistry) is continuously being conducted all over the world to improve the understanding
of the sources and the effects of radiation exposure. Scientists regularly publish their most recent findings in
peer-reviewed journals, or in other types of publication (e.g., governmental publications and books) to ensure
that these findings will provide a better understanding of ionizing radiation sources and effects. All of these
publications create a bank of knowledge that is further reviewed and synthesized by scientific experts who
come to a consensus on the current understanding of the available scientific information.
Exposure to radiation occurs from several sources (see Figure 1 and Table 1) such as:
a. natural background radiation (from the sun, earth and the food we eat)
b. medical screening, diagnostic and therapeutic procedures (e.g., CT scan and radiotherapy)
c. nuclear weapons testing fallout
d. nuclear electricity generation
e.
occupations that entail increased exposure to man-made or naturally occurring sources.
Figure 1. Source of Radiation to which an Individual is Exposed in Everyday Life
Total Dose: 3.0 mSv/year (1)
Natural radon 42%
Natural cosmic 13%
External terrestrial 16%
Natural ingredient (food ingested) 9%
Medical 20%
Nuclear power production ≤ 1%
According to the united Nations Scientific Committee on the Effects of Atomic Radiation (uNSCEAR,
2008), the total annual dose from all sources, averaged over the population of the world, is 3.0 mSv in
total. Over 80% of this dose comes from natural sources with about half from radon and radon decay
products (RDPs). Medical exposure of patients represents 20% of the total dose, whereas all other artificial
sources – fallout, consumer products, occupational exposure, and nuclear power production – represent less
than 1% of the total value.
Annual radiation doses of workers are limited in most countries to 50 mSv/year or less. Only a small fraction
of the work force exceeds 20 mSv/year. The dose limit for the public is set at 1 mSv/year. It is unlikely that
any member of the public would receive more than a fraction of this dose in a year from artificial sources of
radiation. However, doses to patients in some diagnostic procedures may be around 10 mSv. The annual dose
of radiation emitted by certain consumer products, such as smoke detectors and luminous watches, is at the
most 1 µSv or 1/1000th of one mSv.
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Table 1.
average annual Dose to the world Population From all Sources of Radiation (1)
Source
Dose (mSv)/year
Natural
Cosmic
0.39
Gamma Rays
0.48
Internal
0.29
Radon
1.26
artificial
Medical
0.60
Atmospheric Nuclear Testing
0.005
Chernobyl
0.002
Nuclear Power
0.0002
Total (rounded)
3.0
Health risks to radiation-exposed populations are assessed using different types of epidemiological studies.
These studies serve as the basis for implementation of mitigating measures to reduce the assessed risks.
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3.0
3.1
oVERVIEw
what is Epidemiology?
Epidemiology is the study of factors affecting the distribution and determinants of diseases in human
populations. It serves as the foundation for public health and preventive medicine. Epidemiology is based on
observations, rather than on experiments, which can lead to the introduction of varying degrees of bias. A
well designed epidemiological study will try to minimize these potential biases.
There are three main types of epidemiological studies: cohort studies, case-control studies and descriptive eco­
logical studies. The first two types are analytical while the third one is descriptive. In order to be able to assess
the risks associated with exposure (e.g., cancer) to a certain factor (e.g., ionizing radiation) particular attention
has to be given to the soundness of the study design and to its statistical power. Advantages and disadvantages
for each type of study are listed in Table 2.
Table 2. advantages and Disadvantages of Each Type of Study
Study Type Advantages
Disadvantages
Cohort
(lSS uranium
miners)
Effective in studying rare diseases
logistically difficult, expensive and time-consuming
Exposure precedes the health outcome
Requires a large number of subjects
Ability to evaluate multiple health
outcomes for a given exposure
long follow-up period required
less vulnerable to bias; the most reliable Potential loss of cohort members (for various reasons)
type of study
after several years
CaseControl
(Parental
exposure –
residential
radon)
Detailed histories of exposure and other Vulnerability to selection and recall biases
information can be collected relatively
quickly and easily
useful for rare health outcomes
Difficulty with the collection of accurate and complete
information
Number of subjects can be small and
results can be obtained quickly
Difficulty with selection of appropriate control group and
matching on variables
Relatively inexpensive
less reliable than cohort studies
Ability to identify more than one risk
factor
Descriptive
Ecological
(leukaemia
in children
– People
living close
to nuclear
power
plants)
Relatively simple, easy and inexpensive
to conduct
Precision of the statistics may be limited due to the small numbers of observed and expected cases or deaths
Although not exposure specific, can
evaluate a wide range of exposures
Results are averaged over a group, not on an individual level
Often rely on pre-existing data
“Individual” exposures are not known
Does not consider multiple risk factors (i.e., smoking, diet, exercise, etc.)
Impossibility to draw conclusions on causal factor associ­
ated with a disease
Potential errors in the assignment of place of residence
Difficulty in interpreting results; less reliable than case-
control studies
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3.2
The Three Main Types of Epidemiological Studies
3.2.1
Cohort Studies
Cohort studies are analytical studies. They start with a defined group of individuals (the cohort) who are
free of disease, but who vary in exposure to a risk factor within a defined period of time. Individuals within
the cohort are classified according to their exposure. Exposed individuals are assumed to represent all
persons exposed to the risk factor in a given population. unexposed individuals are assumed to represent all
unexposed persons in the same population. Cohort studies are “prospective” which means that they start at the
moment of exposure and follow the individuals in time to determine if they develop a disease. More than one
disease can be studied at a time.
Cohort studies can assess if there is a relationship between a risk factor to which individuals have been exposed
and the development of a disease, e.g., it can assess if there is a relationship between ionizing radiation exposure
and cancer.
Cohort studies measure the relative risk (RR). The RR is the ratio of the risk of an event (e.g., death or cancer
incidence) in the exposed group (i.e., workers with radiation exposure) over the risk in the non-exposed group
(i.e., workers with no radiation exposure). A RR that has a value close to 1 indicates that the risk of the event
is the same in the two groups. A RR less than 1 indicates that the risk of the event is lower in the exposed
group. A RR greater than 1 indicates that the risk of the event is greater in the exposed group.
Cohort studies are the strongest type of epidemiological study. The life Span Study (lSS) of the atomic bomb
survivors and the studies of uranium miners exposed to radon decay products are examples of cohort studies.
3.2.2
Case-Control Studies
Case-control studies, unlike cohort studies, tend to focus on a single disease. Individuals recently diagnosed
with a disease (the cases) are compared with individuals who do not have the disease (the controls). The con­
trol individuals are matched with the cases for different factors (such as age, sex and the opportunity of having
been exposed to the studied risk factor) and are representative of the general population.
Case-control studies are retrospective since they look back in time to determine the risk factors related to the
incidence of the disease. The methods used to collect the data are similar for the cases and the controls. The
main purpose of this type of study is to establish if a risk factor has a causal relationship with a disease. In
case-control studies, risk is expressed as “odds ratios”.
Case-control studies are the second strongest type of epidemiological study. The studies that assessed the
relationship between childhood leukaemia and parental pre-conception exposure, and the studies that assessed
of the relationship between lung cancer and residential radon exposure are examples of case-control studies.
3.2.3
Descriptive Ecological Studies
Descriptive ecological studies compare the occurrence of a specific disease within a population at a certain
time in a given geographical area to the “expected” occurrence of the disease in a stable reference population
(such as the general population of Canada). Results from ecological studies are for a whole population or
groups of people; they do not give information on individuals. For this reason, they cannot serve to draw
conclusions on a causal relationship between an individual’s exposure to a risk factor and a disease outcome;
thus, these studies are only used to generate hypotheses.
In ecological studies, Standardized Mortality Ratios (SMR) and Standardized Incidence Ratios (SIR) are
commonly used for comparison. They represent the ratio of the observed number of deaths (for SMR) or
cases (for SIR) to the number of deaths or cases expected based on what occurs in the larger and stable
reference population. A ratio of 1 indicates that the observed number of deaths or cases for the study
population is the same as the expected number in the reference population.
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The confidence interval evaluates whether the difference in rates between the study population and the
reference population are real or are due to chance. If the confidence interval does not include 1 (1 means
no difference in risk), the ratio (SMR, SIR) for the study population is considered significantly statistically
different from that for the reference population. If the confidence interval includes 1 the study population
is considered no different from the reference population. When a SMR/SIR is based on few observed cases
or deaths, the confidence interval can be very wide. In these situations, cautious interpretation of findings is
necessary since a few cases/deaths can result in large variations in the SMR or SIR. The difference between a
statistically significant and a non-significant finding can be based on just one or two cases or deaths.
Descriptive ecological studies are the weakest form of epidemiological studies. This is why they can only be
used to generate hypotheses regarding risk factors within the population and disease. Most studies of people
living in the vicinity of nuclear power plants (NPPs) are descriptive ecological studies.
3.3
Causation
3.3.1
what is Causation? Does Factor a Cause Disorder B?
A causal relationship can very rarely be established based on a single study. Evidence from many sources of
information (i.e., other epidemiological studies, health physics, radiation biology, laboratory experiments or
animal studies) has to be taken into account. In order to establish causation, it has to be proven that a specific
factor causes a disease. In 1965, Sir Bradford-Hill (2) established a set of nine criteria to establish the causal
link between a specific factor and a disease. These criteria are:
1. Temporal Sequence: Exposure always precedes the outcome. This is the only absolutely essential criterion.
2. Strength: The stronger the association, the more likely it is that the relation of “A” to “B” is causal.
3. Biological Gradient (Dose-Response): An increasing amount of exposure increases the risk. If a doseresponse relationship is present, it is strong evidence for a causal relationship.
4. Consistency: The association is consistent when results are replicated in studies in different settings using
different methods.
5. Biological Plausibility: The association agrees with existing biological and medical knowledge.
6. Consideration of Alternate Explanations: It is always necessary to consider multiple hypotheses before
making conclusions about the causal relationship.
7. Experiment: similar effects are observed in carefully controlled experiments or in other biological models.
8. Specificity: a single supposed cause produces the specific effect. When specificity of an association is
found, it provides additional support for a causal relationship.
9. Coherence: The association should be compatible with existing theory and knowledge.
These criteria are used to scientifically determine valid causal connections between potential disease agents
and the many diseases that afflict humankind. These criteria are used to evaluate, for example, whether
ionizing radiation exposure causes cancer.
3.3.2
what is Correlation?
Correlation is a statistical measurement of the relationship between two variables (e.g., radiation exposure and
cancer incidence). Possible correlations range from -1 to +1. A zero correlation indicates that there is no linear
relationship between two variables. A correlation of -1 indicates a perfect negative linear correlation, meaning
that one variable goes up, and the other goes down. A correlation of +1 indicates a perfect positive linear
correlation, meaning that both variables move in the same direction together.
“Correlation does not imply causation” is a phrase used in science and statistics to explain that correlation
between two variables does not automatically imply that one causes the other.
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3.3.3
Errors that have an Impact on the accuracy of Risk Estimates in Epidemiology
The validity of a study is dependent on the degree of systematic error. A systematic error is an error that is
constant in a series of repetitions of the same experiment or observation. The two important systematic errors
that can affect the validity of a study in epidemiology are the presence of bias and confounding factors. A well
designed study will attempt to minimize these errors.
a. Bias: A bias is an error in the design of a study that can influence the results or conclusions of the study.
It could mask the true association between the exposure and the disease. For example, the manner the
subjects are selected for a study (which is called selection bias) can have an influence in the estimate of
association between a risk factor and a disease.
B. Confounding Factor: A confounding factor is associated with both disease and exposure. For example,
when studying the relationship between occupational RDP exposure and lung cancer, the true effect of
radon exposure can be masked by a third factor which is a confounding factor (e.g., age and sex). Age and
sex are both associated with lung cancer and occupational RDP exposure. These factors must therefore be
controlled for in a study of the relationship between occupational RDP exposure and lung cancer.
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4.0 STUDIES oN whICh EPIDEMIoLoGICaL EVIDENCE oF
RaDIaTIoN hEaLTh EFFECTS IS BaSED
The epidemiological evidence of radiation-related health effects comes from several main research populations.
These include the atomic bomb survivors, people involved in the Chernobyl disaster, patients treated with
radio-therapy for non-cancer diseases, miners exposed to radon decay products and nuclear energy workers.
This section provides a brief overview of these study populations and summarizes what has been learned
about the health effects of exposure to radiation from these populations.
4.1
atomic Bomb Survivors Life Span Study
The life Span Study (lSS) on the life-long follow-up of the Japanese atomic bomb survivors was developed
after the 1945 bombing of Hiroshima and Nagasaki. It is the largest, most comprehensive and most detailed
cohort study ever performed, with more than 60 years of follow-up after radiation exposure. The results of
this study are the most important source of scientific information on the health effects of ionizing radiation
exposure (primarily high doses and high dose rates) on which today’s radiation protection regulations are
largely based.
The lSS is comprised of over 120,000 people, and includes both sexes and all age groups. Since the dose rate
decreased over the distance from the blast, the whole body dose range was large and permitted an assessment
of the risk of different types of cancer. Mortality data from 1950 to 1997 has been assessed in detail and
reported in international scientific publications.
To date the lSS results are:
•
The main radiation effect observed in the lSS is cancer (both solid cancers and leukaemia).
•
The excess risk of cancer increases as the radiation dose increases.
•
Clinical studies of some of the lSS survivors have also demonstrated that radiation dose is clearly
associated with the incidence of thyroid disease, benign tumour of the uterus, hypertension, chronic
liver disease and cirrhosis.
•
Studies of survivors’ offspring conceived after the bombings have shown no excess of congenital ab­
normalities (birth defects), mortality, or cancer incidence when followed up through to the late 1990s.
•
In contrast, radiation exposure of a foetus (during pregnancy) has been related to an increased
incidence of cancer in adulthood, small head size and mental retardation in infants.
The lSS data has been used for the construction of models describing how radiation-induced cancer risk varies
according to dose, as well as with factors such as age at exposure, time since exposure and sex. The incidence
of solid cancers and leukaemia from the atomic bomb survivors’ studies gives some of the best evidence of the
linear no-threshold dose response hypothesis (or the lNT hypothesis) down to doses of about 100 mSv.
The lSS has also been used to investigate the incidence of non-cancer health effects. Radiation exposure can
increase the risk of diseases, particularly cardiovascular diseases, such as heart disease and stroke, in people
exposed to high doses (greater than 1,000 to 2,000 mSv). According to uNSCEAR 2008 (1), there is no
evidence that there is an increased risk of non-cancer diseases at doses lower than 500 mSv.
4.2
The Chernobyl accident
The accident at the Chernobyl nuclear power plant in 1986 is the most severe accident in the history of the
nuclear power industry. large areas of Belarus, ukraine and the Russian federation were contaminated with
radionuclides released from the accident.
•
The highest radiation doses were received by emergency workers and on-site personnel, in total about
1,000 people, during the first days of the accident.
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•
The majority of the residents (over 5 million people) of the contaminated areas were exposed to relatively
low whole-body doses of radiation, not much higher than doses due to natural background radiation.
Now, over 20 years later, international agencies have reviewed the health, environmental and socio-economic
consequences of the accident (3, 4, 5). The conclusions from this review are:
•
A hundred and thirty-four emergency workers were diagnosed with acute radiation syndrome within
the first few days. Twenty-eight of these workers died within the year and three additional workers
died shortly thereafther.
•
Approximately 4,000 thyroid cancer cases were diagnosed in children and adolescents who were ex­
posed at the time of the accident. Doses of radioactive iodine to the thyroid, received in the first few
months after the accident, were particularly high for children who drank milk containing high levels
of radioactive iodine. More cases can be expected during the next decades among those children who
were exposed at the time of the accident. According to uNSCEAR 2008 (1), there were 15 reported
deaths up until 2005.
•
Apart from the increase in thyroid cancer incidence among those exposed at a young age, there is no
clearly demonstrated increase in the incidence of solid cancers or leukaemia due to radiation in the
most affected populations. There is also no scientific evidence of an increase in rates of other diseases.
•
Nonetheless, a significant psychological and social impact was observed as a result of the accident.
In contrast with the Chernobyl accident, the event that happened at the Three Mile Island nuclear power plant
in Pennsylvania, united States, in 1979, is an example of an accident that successfully avoided releases of
radioactivity in the environment and exposures to the public. The Kemeny Commission, established to shed
light on the accident, concluded the following: “There will either be no case of cancer or the number of cases
will be so small that it will never be possible to detect them. The same conclusion applies to the other possible
health effects.” (6)
4.3
Patients Treated with Radiotherapy for Non-Cancer Diseases
up to the 1960s, many patients were treated with radiotherapy for non-cancer diseases, such as painful
degenerative joint disorders, tennis elbow, and autoimmune diseases. Some of these treatments were associated
with a statistically significant increased risk of leukaemia and solid cancers. In 1957, Court-Brown and Doll
(7) analysed the mortality of 14,554 patients treated with radiation and found a ten-fold increase in mortality
from leukaemia in these patients. This conclusion has been confirmed by a follow-up study (8). The findings
from this study are consistent with the lSS findings, together they remain the most important source of
information about radiation-induced leukaemia.
4.4
Miners Exposed to Radon Decay Products
At the end of the 19th century, lung cancer in miners was linked to the exposure to radon, but it was only
recognized in the 1950s that the cause of lung cancer was the radioactive decay products (RDP) of radon.
In 1994, an important combined study (9) of eleven large miner cohorts, including four from Canada (Beaver­
lodge and Port Radium uranium miners, Ontario uranium miners, and Newfoundland fluorspar miners)
assessed the relationship between RDP exposure and lung cancer. The study also included cohorts of miners
from the uSA, Sweden, Australia, the Czech Republic, France, Germany and China. The study revealed that:
•
There was an excess risk of lung cancer mortality attributed to RDP exposure.
•
The risk of lung cancer increased linearly with increasing RDP exposure.
•
Several modifying factors affected this risk. The risk of lung cancer mortality per unit of RDP
exposure decreased with increasing time since exposure, with increasing attained age and with
increasing exposure rate.
•
Tobacco had an important impact on the relationship between RDP and lung cancer risk.
•
lung cancer was the only established health effect of RDP.
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These findings form the basis of today’s radiation protection programs for uranium miners. Based on this
study, the model for assessing RDP risks was adopted by the Biological Effects on Ionizing Radiations VI
(BEIR VI) Committee (10).
Recent updates of the French, German, Czech Republic, Colorado Plateau, and Canadian (Newfoundland
Fluorspar miners and the Beaverlodge and Port Radium uranium miners) miners’ studies (11-20) have in­
creased the statistical power and precision of risk estimates and largely support the BEIR VI risk model (10).
4.5
Effects of Radiation on Nuclear Energy workers – IaRC 15-Country Study
In 2005, the International Agency for Research on Cancer (IARC) released a study (21) on cancer mortality
among nuclear energy workers. The IARC Study included cohorts of workers from 15 countries with a mortal­
ity follow-up from 1957 to 1994. The results from this study were:
•
There was a statistically significant increased risk of mortality from all cancers (excluding leukaemia)
per radiation dose in nuclear workers, based on all 15 countries.
•
The workers from Canada had the highest risks of solid cancer mortality (an excess risk of 6.5 per
radiation dose (Sv)). Their risk estimate was the highest of all of the cohorts and was statistically
significantly higher than the combined risk estimate for all 15 countries studies.
•
The exclusion of the Canadian workers rendered the risk estimates statistically non-significant for the
remaining 14 countries, which was consistent with previous international studies of nuclear energy
workers and with the atomic bomb survivors’ studies.
An earlier study of Canadian workers (22) that used the same source of data (the National Dose Registry) as
the 15-country study, found a sizeable but statistically non-significant increase in risk of solid cancer mortality
per radiation dose for Canadian workers. This apparent discrepancy in the results between the Canadian study
and the 15-country study for the Canadian workers attracted attention and questions from regulatory agencies
and industry.
In order to understand the Canadian workers’ cancer risk estimate in the IARC 15-country study, the CNSC
initiated a preliminary comparison of the two studies in 2005. It was discovered that workers who were
missing information on their socioeconomic status had been excluded from the solid cancer analysis in the
international study. This was the case for about 50% the Ontario Hydro workers’ cohort that represented 50%
of the Canadian nuclear workers, thus Ontario Hydro workers were excluded from the Canadian cohort in the
15-country study. However, SES information was also missing for 40% of Atomic Energy of Canada limited
(AECl) workers; nonetheless, they were not excluded. It was also discovered that workers from AECl, who
now dominated the Canadian cohort in the 15-country study, were missing important historical dose data.
Canadian investigators reviewed the reasons for the missing dose data. Consequently, the CNSC initiated
an in-depth reanalysis of the Canadian nuclear workers’ study using the Ontario Hydro worker data and
corrected AECl worker data. The purpose of this reanalysis was to determine if the corrections could explain
and resolve the initial high solid cancer mortality risk estimates. This reanalysis suggests that there is no reason
to conclude that Canadian workers are at higher risk than any other workers carrying out similar work. The
final results of this independent reanalysis of the Canadian nuclear workers’ cohorts will be available soon in a
report from the CNSC.
4.6
Summary
The above-mentioned studies have contributed to the current scientific understanding of the health effects
from radiation exposure. Based on this understanding, national and international experts have agreed on
principles and practices that best protect workers and the public from the health effects of ionizing radiation
exposure.
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5.0 EPIDEMIoLoGICaL STUDIES oF PEoPLE LIVING NEaR
NUCLEaR PowER PLaNTS oR URaNIUM PRoCESSING FaCILITIES
A tremendous amount of work has been conducted in Canada and internationally to assess the radiation risk
of people living near nuclear facilities. Most of these studies have been descriptive ecological studies which
compare disease rates among populations living near nuclear facilities to disease rates within the general
population. Case-control and cohort studies have also been conducted. This section will discuss some of these
studies in more detail.
It is known that disease clusters (such as childhood leukaemia) do exist near some nuclear facilities, as well
as elsewhere, where no nuclear facilities are located. There are, for example, 264 reported leukaemia clusters
in England, Wales and Scotland (23) and most of them are not in the vicinity of a nuclear facility. Three
main hypotheses have been put forward to explain why clusters have occurred around nuclear facilities. These
include parental pre-conception radiation exposures, environmental exposures from nuclear facilities, and the
Kinlen (24) hypothesis. This latest hypothesis suggests that leukaemia could be explained by the existence of
an infectious agent that is present as a result of population mixing when people migrate to communities near
nuclear facilities. To date, none of these three hypotheses have been proven.
5.1
offspring of ontario hydro workers
5.1.1
Childhood Leukaemia
In Canada, a case-control study (25, 26), based on childhood leukaemia cases from the Ontario Cancer
Registry diagnosed between 1950 and 1988 assessed the relationship between childhood leukaemia and the
father’s ionizing radiation exposure before conception.
This study showed:
•
No statistically significant association between childhood leukaemia and the father’s occupational
exposure to ionizing radiation.
•
No evidence of an elevated leukaemia risk in relation to any exposure period (lifetime, six months
or three month prior to conception) or exposure type (total external whole-body dose of gamma
radiation, tritium dose, or radon exposure).
•
That the results were the same when taking into account the father’s whole-body external radiation or
tritium exposure.
5.1.2
Birth Defects
A case-control study (27) was conducted to evaluate the risk of having a child with a birth defect (also referred
to as a congenital anomaly) as a result of parents (fathers or mothers) pre-conception occupational radiation
exposures.
The study showed:
•
No statistically significant increased risk of having a child with birth defects when the parents were
exposed to radiation before the conception of a child.
These Canadian studies are consistent with other studies of nuclear workers, and provide no evidence of a
causal link between workers’ pre-conception exposure and cancer or birth defects in their children. These find­
ings are consistent with higher-dose studies of atomic bomb survivors and cancer patients who subsequently
became pregnant (28).
5.2
Communities Near Nuclear Facilities in ontario
Several descriptive ecological studies (29, 30, and 31) examined mortality and the incidence of childhood
leukaemia among children aged 0-14 years living in the vicinity of Ontario nuclear facilities. Analyses were
performed separately for each of the nuclear facilities.
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The results of these studies were:
•
No evidence was found of any excess leukaemia incidence or mortality close to the AECl Facilities in
Chalk River or the nuclear power demonstration station in Rolphton.
•
The occurrence of leukaemia in the vicinity of the Bruce and Pickering nuclear generating stations
(NGS) was greater than expected. Similar findings were found prior to the opening of the Pickering
facility. Based on the small number of cases and deaths, and the wide confidence intervals, there
was no statistical evidence that the leukaemia was due to anything but the natural variation in the
occurrence of the disease.
•
The findings for leukaemia cases and deaths were similar.
The rarity of childhood leukaemia and the small number of observed and expected cases and deaths lead to
the limited statistical power of the study.
Another descriptive ecological study (32) compared rates of birth defects, stillbirths, and deaths within the first
year of life among the offspring of residents living within 25 km of the Pickering NGS in Ontario (1971-1988)
with those of the general Ontario population.
The results were:
•
Mortality rates of stillbirth, neonatal mortality and infant mortality were statistically significantly
lower than the Ontario average.
•
Rates of birth defects were generally lower than provincial rates.
The Durham Region Health Department (DRHD) conducted a descriptive ecological study in 2007 to exam­
ine the rates of cancer incidence and mortality, birth defects and stillbirths from 1981 to 2004 in the areas of
Pickering and Darlington Nuclear Generating Stations (NGSs) (33). The Durham Region is unique due to the
presence of a large population (285,000) living within 10 kilometres of two NGSs.
The results of this study were:
5.3
•
This study is consistent with the original analysis conducted from 1979 to 1993 (34) and with two
Snapshot reports for the region on cancer (35) and healthy newborns (36).
•
In general, the rates of cancer incidence and mortality were similar to the Ontario averages; the
prevalence of birth defects was statistically significantly lower, and rates of Down syndrome were
similar to those in the rest of Ontario.
•
Given the extremely low levels of radiation exposures, which included tritium, it is unlikely that any
radiation related effects would be observed.
health Studies in the Port hope Community
Several epidemiological studies have been conducted in Port Hope in the last 30 years, covering the time period
from the 1950s to the present day.
In 2009, the CNSC published a report: Understanding Health Studies and Risk Assessments Conducted in the
Port Hope Community from the 1950s to the Present (37). This report used a weight of evidence approach
to assess the health effects within the community looking at toxicological and radiological properties of the
contaminants within the town. Over thirty environmental studies, thirteen epidemiological studies conducted
in Port Hope, and over forty international studies were reviewed in the report.
Based on the radiological and non-radiological contaminants present in the community, the plausible health
effects considered were: lung cancer (due to radon exposure), bone cancer (due to radium exposure above a
threshold dose of 10 Sv) and kidney disease (due to uranium toxicity).
The descriptive studies reviewed in the CNSC report compared the overall health status of Port Hope residents
with that of residents in other similar communities, and with the general Ontario or Canadian population. The
rates of mortality, cancer incidence, and birth defects were assessed.
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The main conclusions from this review were:
•
Overall, mortality from all cancers in Port Hope was statistically similar to the general Ontario
population.
•
Childhood cancer mortality and birth defects were statistically similar to the general population of
Ontario.
•
Overall cancer incidence in Port Hope was statistically similar to the general Ontario population and
similar communities.
•
No statistically significant excess of kidney disease mortality or statistically significant excess of bone
cancer incidence or mortality in residents was demonstrated during the period when the radium and
uranium refining and processing industries were in operation in Port Hope.
•
A statistically significant excess of lung cancer incidence was found in Port Hope women between
1986 and 1996, but no excess risk was found in men or women in other time periods.
A case-control study conducted in Port Hope assessed the relationship between lung cancer (38, 39) and
residential radon in Port Hope.
The study concluded:
•
There is no conclusive link between residential radon and lung cancer rates, even among people living
in homes with levels of radon identified as “high” in the study.
Finally, approximately 3,000 radium and uranium processing workers from Port Hope (20, 40) were assessed
to determine the relationship between occupational radiation exposure (RDP and gamma radiation dose) and
mortality and cancer incidence. Workers were followed for 50 years for mortality and for 30 years for cancer
incidence.
The study concluded:
•
Port Hope workers are as healthy as the general male population of Canada.
•
No statistically significant relationship was found between Port Hope worker’s radiation exposures
and any cause of death or cancer incidence. This was largely due to the relatively low occupational
radiation exposures of these workers.
Findings concerning Port Hope residents and workers are consistent with findings from over 40 epidemio­
logical studies conducted elsewhere in the world analyzing the health status of workers and the public exposed
to the radium and uranium refining and processing industry.
5.4
Communities Near Gentilly-2 in Québec
In 2003, the “Régie régionale de la santé et des services sociaux de la Mauricie et du Centre-du-québec”
published the results of a study (41) on the cancer incidence and mortality in the vicinity of Hydro-québec’s
Gentilly-2 nuclear power plant between 1994 and 1996. The study compared the rates of cancer incidence
and mortality in the vicinity of Gentilly-2 with the general population of québec. The study looked at the
incidence of the ten most common cancers, as well as thyroid cancer and leukaemia in the overall population
and the ten most common cancers in children (aged 0 to 19 years old).
The study concluded:
•
There was no excess risk of cancer in the Gentilly-2 area compared to the general québec population.
•
The cancer rates among boys were similar to the general québec population.
•
Women had lower rates of cancer compared to the general québec population, especially for lung and
breast cancer.
The study was based on few cases and this means it should be interpreted with caution. This is especially true
for the youngest group (aged 0-19 years old) for whom the rareness of childhood cancers resulted in variations
in disease rates in the different geographical areas of the province of québec.
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5.5
Summary
In summary, Canadian studies provide no evidence of statistically significant excess rates of cancer, childhood
cancers, birth defects, stillbirths or infant mortality related to the operation of Canadian nuclear facilities.
5.6
Communities Near German Nuclear Facilities
5.6.1
Studies Conducted around Nuclear Power Plants
In 1992, a case-control study (42) looked at the incidence of childhood cancer within the 15 km radius of 20
West Germany nuclear installations that had started to operate between 1960 and 1988.
This study found:
•
No increased risks of all cancers including leukaemia in children less than 15 years of age within the
15 km zone of the nuclear plants.
•
Statistically significant increased risks of leukaemia in children less than five years of age living less
than five km from the installations, especially those living in the neighbourhood of installations that
started to operate before 1970.
However, this increase could not be explained by radiation exposure. In addition, an even more pronounced
increase in childhood leukaemia was observed in regions where no nuclear power plants (NPPs) were operating.
This study was further updated to include the period from 1991 to 1995 (43). It was not able to reproduce the
original results and only found a tendency towards an increased risk of acute leukaemia in children younger
than five years of age within the five km radius of an installation. This finding was strongly influenced by the
cluster near the Krümmel NPP.
Another study (44) was initiated in 1999 to compare cases of childhood leukaemia in the vicinity of Krümmel
NPP and in the vicinity of the Savannah River Site (SRS) in South Carolina, uSA. It was thought that the
German cluster was related to tritium discharges.
This study found:
•
The amount of tritium released by the SRS facility exceeded several times the amount of tritium
released by the Krümmel NPP.
•
No cluster of childhood leukaemia was found at the SRS.
•
The excess of childhood leukaemia near the Krümmel NPP cannot be explained by tritium discharges.
A further study in the region of Hamburg, which is located 30 km from Krümmel (45), looked at the child­
hood leukaemia incidence for the period of 1990 to 2005. This study found:
•
Elevated rates of childhood leukaemia had persisted in this community for more than 15 years (since
the first study conducted in 1992).
The cluster observed near Krümmel is the largest childhood leukaemia cluster reported to date worldwide.
5.6.2
Case-Control Study on Leukaemia in German Children (KiKK)
As a response to concerns resulting from the above mentioned studies, the German Federal Office for Radia­
tion Protection (BfS) initiated in 2003 a case-control study of children less than five years of age. This study,
named the KiKK study, was based on the German Childhood Cancer Registry (GCCR) and looked at all
childhood cancer cases diagnosed between 1980 and 2003 compared to control children without cancer. The
KiKK study (46) used distance from a NPP as a substitute for radiation exposure to evaluate the risk of child­
hood cancer and focused on cases within the 5 km zone of the 16 NPPs in Germany.
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The main finding was:
•
An increased risk of leukaemia in children less than five years of age with decreasing distance from a NPP.
A follow-up to the KiKK study (47) was conducted. The study focused only on the childhood leukaemia cases registered between 1980 and 2003.
The study concluded that:
•
The risk of leukaemia in children less than five years of age increased the closer their home was to a
NPP. The results were consistent for all 16 nuclear power sites.
A further follow-up to the KiKK study (48) collected information on other risk factors of childhood
leukaemia to help explain the earlier findings.
The study concluded that:
•
The observed trends in childhood leukaemia decreased over time.
•
There was no clear causal explanation for the childhood leukaemia.
No estimates of radiation exposures from the plants were available, therefore distance (between home and
reactor) was used as a substitute for radiation exposure. Nonetheless, the relationship between childhood
leukaemia and distance from the NPPs cannot be explained by the radiation exposure from these plants.
Environmental exposures during routine operations were extremely low, especially compared to natural
and other ionizing radiation sources, and the findings were not consistent with the current understanding
of radiation effects observed in radiation biology and epidemiology. In light of this, the observed positive
distance trend remains unexplained and no statements on the causes of the increased cancer rates can be made,
according to the BfS and GCCR.
5.6.3
The German Radiological Protection Commission
The KiKK Study raised considerable public concern and scientific debate. The German Radiological Protection
Commission reviewed the findings of the KiKK study using an interdisciplinary working group of international
experts. The working group task was to review the data and make a final evaluation of the study’s overall design,
conduct, results and interpretation (47, 49).
The main conclusions of the working group are summarized as follows:
•
There are several weaknesses in the methods used to estimate radiation exposure and to identify other
potential influencing factors.
•
The evidence of increased childhood cancer risks was limited to a 5 km zone around the NPPs.
•
The study examined distance from the NPP and not radiation exposure; distance is not a suitable
substitute for radiation exposure.
•
The natural radiation present within the study area was greater by several orders of magnitude than
the radiation emissions from the NPPs.
•
The actual radiation emissions from the NPPs cannot explain the KiKK results.
•
The KiKK study was not able to survey other risk factors, thus cannot be used to help explain the
causal reasons for the relationship between distance and leukaemia.
•
Finally, studies conducted in other countries were not able to produce similar findings.
In conclusion, the German Radiological Protection Commission working group found no evidence of a
causal relationship between radiation and childhood leukaemia among children less than 5 years of age
within 5 kilometres of the German NPPs.
In summary, the reason for the increased childhood leukaemia rate around German NPPs is unclear. However,
the increased rates could not be explained by the actual radiation emissions from the German NPPs. Since
childhood leukaemia is thought to be caused by several factors, other factors may have been responsible for
the observed results. More extensive, interdisciplinary research on the causes and mechanisms of the develop­
ment of childhood leukaemia is required to fully understand the disease.
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5.6.4
Reviews of Studies of Childhood Leukaemia around Nuclear Facilities
Numerous literature reviews of epidemiological studies of childhood leukaemia around nuclear facilities have
been conducted over the years. laurier et al. conducted several comprehensive literature reviews of studies of
childhood leukaemia in the vicinity of nuclear sites. The most recent review (50) included 198 local nuclear
sites in 10 countries and 25 multiple site studies in 8 countries concluded that:
•
Out of all the studies, there were only three confirmed clusters: one in Sellafield (West Cumbria) near
the reprocessing plants, one in Dounreay (Scotland) and one in the village of Elbmarsch near the
Krümmel NPP (Germany). These three clusters have persisted over time.
•
The clusters cannot be explained by environmental radiation exposures near the nuclear facilities.
•
None of the multi-site studies indicated an increased risk globally.
laurier et al concluded that the Kinlen hypothesis is the most convincing hypothesis for disease clusters;
however, this infectious agent has yet to be found. Many additional risk factors associated with childhood
leukaemia (e.g., genetic pre-disposition, nutrition, gestation and other environmental factors) should be
considered. Only large-scale national or international analytical studies would be able to characterize the
origins of such clusters and clarify the main risk factors for childhood leukaemia. Finally, their review
emphasized that the KiKK studies were not supported by studies in other countries, and that to date nothing
can explain the excess risk observed.
5.7
Committee on Medical aspects of Radiation in the Environment Reports
5.7.1
Childhood Leukaemia around Nuclear Power Plants
In 1983, the uK Government set up the Black Advisory Group to look at the presence of an unexpected
excess of childhood leukaemia cases in Seascale, a village located 3 km from the Sellafield nuclear fuel
processing plant. The Black Advisory Group found no explanation for such an excess. In 1985, The uK
Department of Health and the Health and Safety Executive (HSE) established the Committee on Medical
Aspects of Radiation in the Environment (COMARE) to monitor these kinds of findings. COMARE
produced three separate reports on the incidence of childhood leukaemia around NPPs in 1996 (51), 2005 (52)
and 2006 (53), using the National Registry of Childhood Tumours.
COMARE’s conclusions were:
•
leukaemia and many other types of childhood cancers did not occur evenly within the population of
Great Britain and these differed more than would be expected from simple random or chance variations.
•
There was no evidence of excess childhood cancer around NPPs, although some clusters existed and
persisted over time near other nuclear installations (e.g., the Sellafield reprocessing plant).
•
Since disease clustering was found in many locations with and without NPPs, other factors in the
environment needed to be considered.
Based on the Bradford-Hill criteria, COMARE concluded there was no evidence that increased childhood
leukaemia rates were due to the radiation discharges from the facilities.
5.7.2
Effects of Radiation on offspring of Nuclear workers
In 1990, Gardner et al. conducted a case-control study (54) on leukaemia and lymphoma among young people
living near the nuclear fuel processing plant in Sellafield, uK. They concluded that the increased incidence
of leukaemia and Non-Hodgkin lymphoma (NHl) among the children was associated with parental
occupational radiation exposure prior to child conception.
COMARE also extensively reviewed epidemiological studies, laboratory and genetic research related to
possible biological mechanisms for childhood leukaemia in their 1996 (51) and 2002 (55) reports.
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COMARE concluded that:
5.8
•
There was no evidence of a causal relationship between the workers’ radiation exposure and cancer or
birth defects in their children.
•
These findings were consistent with high dose studies of the atomic bomb survivors and radiotherapy
patients who become pregnant.
Summary
In summary, the many epidemiological studies of populations living in the vicinity of nuclear facilities have
provided no substantive evidence that any adverse health outcomes are related to environmental radiation
exposures from these facilities. The current levels of environmental or occupational radiation exposures in
Canada are low. There is no evidence of increased birth defects, cancer incidence or mortality in populations
due to these radiation exposures.
Three leukaemia clusters have been identified in the vicinity of the three nuclear facilities located in England,
Germany and Scotland. It would be necessary to conduct large-scale national and international analytical
studies to be able to characterize the origins of these clusters and to clarify the main risk factors for childhood
leukaemia.
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6.0 INTERNaTIoNaL GRoUPS oF ExPERTS IN RaDIaTIoN
PRoTECTIoN
6.1
United Nations Scientific Committee on the Effects of atomic Radiation
The united Nations Scientific Committee on the Effects of Atomic Radiation (uNSCEAR) was established in
1955. The mandate of the Committee was to undertake broad reviews of the sources of ionizing radiation and
its effects on health and the environment. uNSCEAR has since become the world authority on global levels
and effects of ionizing radiation.
uNSCEAR reviews all new information on radiation levels and effects and synthesizes it into a coherent
picture for use by policy makers and other stakeholders. These reviews are the scientific foundation used by the
International Commission on Radiological Protection (ICRP) in developing its recommendations on radiation
protection, and by other agencies such as the International Atomic Energy Agency (IAEA), in formulating the
international Basic Safety Standards (BSS) for protection against ionizing radiation.
uNSCEAR is composed of delegations from 21 countries. Each delegation contributes to the work of the
Committee by providing specific expert knowledge on a broad range of issues in the field of radiation sources
and effects, and competent assessment of draft scientific documents. The CNSC has two members on the Can­
adian delegation to uNSCEAR.
6.2
The Biological Effects on Ionizing Radiation Committee
The united States (u.S.) National Academy of Sciences Committee on the Biological Effects of Ionizing
Radiation (BEIR Committee) reports directly to the u.S. government on the health effects of low-level
ionizing radiation. The Committee reviews the latest findings on ionizing radiation and presents its conclusions
in reports. The most recent report from this Committee is the BEIR VII Report: Health risks from exposure to
low levels of ionizing radiations (2005) (56).
The BEIR VII Committee was given the mandate to develop “risk models” for estimating the relationship
between exposure to low dose levels of ionizing radiation and its harmful health effects. After a thorough
review of the most recent literature available, the BEIR VII Committee concluded that:
•
The linear no-threshold model (lNT) provides the most reasonable and a very conservative
description of the relation between low-dose exposure to ionizing radiation and the incidence of
solid cancers. It assumes there is a direct relationship between radiation exposure and cancer rates.
•
There is a dose-response relationship at doses in the order of 100 mSv or more delivered at high dose
rates.
BEIR VII also reported that at low doses (less than 100 mSv), there is no clear scientific evidence of
any adverse health effects. likewise, the presence of other risk factors (e.g., age, sex, genetics, and other
behavioural and environmental risk factors) can make it difficult to separate the effects due only to radiation
from the effects from other risk factors. Nonetheless, the linear No-Threshold model (lNT) is a risk model
used internationally by most health agencies and nuclear regulators to set dose limits for workers and members
of the public. Because the lNT assumes all radiation exposures carry some risk, in addition to dose limits,
licensees are required to keep radiation exposures as low as reasonably achievable (AlARA). This is a core
principle of the CNSC’s approach to radiation protection. Thus, the lNT model plays a key role in how the
Canadian Nuclear Safety Commission (CNSC) approaches radiation protection.
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6.3
The International Commission on Radiological Protection
The International Commission on Radiological Protection (ICRP) is an advisory body providing recommen­
dations and guidance on radiation protection. The ICRP publishes its recommendations and advice in the
fields of medicine and physics in the shape of a scientific journal, entitled the Annals of the ICRP.
In preparing its recommendations, the ICRP considers the fundamental principles and the scientific results
upon which appropriate radiation protection measures can be established, while leaving to the various national
protection bodies the responsibility of formulating the specific advice, codes of practice, or regulations that
are best suited to the needs of their individual countries. While the ICRP has no formal power to impose its
recommendations, legal authorities in most countries adhere closely to the ICRP recommendations.
As the leading group in radiation protection, the ICRP has formulated a practical working system of radiation
protection that is scientifically based on straightforward assumptions. CNSC adheres to the ICRP system. The
most recent recommendations from the ICRP (2007) are set out in ICRP 103 (57).
6.4
The International atomic Energy agency
The International Atomic Energy Agency (IAEA) is the world’s centre of cooperation in the nuclear field. The
Agency works with its 151 Member States and multiple partners worldwide to promote safe, secure and peace­
ful nuclear technologies.
The IAEA helps countries to implement nuclear safety and to prepare for and respond to emergencies. Their
mandate is to protect people and the environment from harmful radiation exposure. The IAEA’s work has set
a framework to which Canada adheres. This framework includes advisory international standards, codes and
guides; binding international conventions; international peer reviews to evaluate national operations, capabil­
ities and infrastructures; and an international system of emergency preparedness and response.
The IAEA safety standards provide a system of fundamental safety principles, safety requirements and safety
guides for ensuring safety. They reflect an international consensus on what constitutes a high level of safety for
protecting people and the environment from harmful effects of ionizing radiation.
The IAEA Statute makes the safety standards binding on the IAEA in relation to its own operations. Any
State entering into an agreement with the IAEA concerning any form of Agency assistance is required to
comply with the requirements of the standards that pertain to the activities covered by the agreement.
The principal IAEA safety guide is the Basic Safety Standards (BSS) which are currently undergoing revision.
The BSS is based upon the latest recommendations of the International Commission of Radiological
Protection (ICRP) and applies to three categories of exposure: occupational exposure, public exposure and
medical exposure. The BSS is written in legal terminology such that states can take sections of the BSS
verbatim and include it in their radiation protection regulations. Canada has contributed to the drafting of the
BSS although our radiation protection regulations were developed directly from the ICRP recommendations
and so do not directly mirror the BSS text.
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7.0
DISCUSSIoN aND CoNCLUSIoNS
7.1 how Does the CNSC Use Epidemiology To Protect Nuclear workers and the Canadian
Public?
The CNSC’s mandate is to regulate the use of nuclear energy and materials to protect the health, safety and
security of Canadians and the environment.
To meet this objective, the CNSC sets regulatory limits on radiation exposures for workers and the public
on the basis of ICRP’s recommendation. These limits are outlined in the Canadian Radiation Protection
Regulations (58). The CNSC also produces guidance documents to help licensees implement a radiation
protection program and other measures (e.g., action levels) that keep the amount of exposure to ionizing
radiation as low as reasonably achievable (AlARA).
The purpose of these regulatory limits and guidance documents is to prevent health effects and to establish an
acceptable level of safety for workers and members of the public. The primary concern is the minimization of
radiogenic cancers. Setting adequate protective exposure limits and providing appropriate guidance requires an
assessment of risks.
The health effects of radiation have been extensively studied. Epidemiological studies based on good quality
radiation exposure data are the best source of evidence for assessing human health risks from radiation
exposure. Cohort studies are the strongest type of epidemiological study and provide the strongest evidence
of the relationship between radiation exposure and health effects. However, even cohort studies have a limited
ability to assess health risks at low exposures. This is the reason why at low doses, very large populations, high
quality individual exposure information, and the control of biases and confounding factors are essential. Thus,
at low doses, it becomes absolutely necessary to understand the mechanisms of the onset of cancer through
the study of radiation biology.
The CNSC staff keeps its knowledge up to date through the coordination of national epidemiology studies
of radiation workers (e.g., Eldorado uranium workers, Ontario miners, AECl reanalysis), the review of
recent multi-disciplinary research (such as genetics, molecular biology, health physics and epidemiology
in peer-reviewed scientific publications), participation in multi-disciplinary international committees of
experts (e.g. uNSCEAR, IAEA), and the review of the documents produced by BEIR, the ICRP and other
authorities involved in radiation risk assessment. In this process, the CNSC bases its decisions on objective
scientific information from reports by scientific advisory bodies including uNSCEAR, the ICRP, and the
BEIR Committee, with additional input from its own independent review of the literature, and the results of
CNSC funded research.
The shape of the dose response curve for cancer at low doses is a matter of considerable scientific debate.
Hypotheses range from beneficial effects of small radiation doses (hormesis) to a threshold response, or to a
no-threshold supra-linear response (implying that small doses are more hazardous than previously assumed).
The CNSC bases its risk assessments for populations exposed to low level of ionizing radiation on the linear
no-threshold (lNT) hypothesis, which assumes that the risk of cancer due to a low dose is proportional to
dose, with no threshold. The use of lNT for radiation protection purposes has been repeatedly endorsed by
authoritative scientific advisory bodies, including uNSCEAR, the ICRP and the BEIR Committees, and
remains the best model on which to base radiation protection regulations. However, it should be noted that
BEIR VII also recognizes that the use of this model might over estimate (for example, the overestimation of
the predictions on the excess risks of cancer following the Chernobyl accident) the risk at low doses making it
conservative and suitable to protect the health of workers and the public.
Although recent radiobiological findings indicate that cellular repair processes could happen at low doses,
these findings are not understood well enough to trigger changes in the current regulations. lNT is still
supported by data from both epidemiology and radiobiology and provides a conservative, precautionary
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assessment of risk at doses below 100 mSv. At doses below 100 mSv, it is not possible to distinguish disease
attributed to radiation from that of the natural variation in disease among the general population.
The Radiation Protection Regulations exposure limits for the Canadian public are set at 1 mSv/year, and at
50 mSv annually, or at a maximum of 100 mSv for five years, for workers. These limits, in addition to the
AlARA principle, are included in the Radiation Protection Program required by the CNSC for each licensee.
Any radiation exposure to Canadian nuclear workers or the public, as a result of the nuclear industry, are thus
limited to exposure levels well below the regulatory limits. This ensures that Canadians are safely protected
from ionizing radiation health effects.
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